During maneuvers and other types of flight conditions, an aircraft propulsion system typically requires varying rates of fuel flow. Fuel control systems have therefore been developed that provide varying fuel flow rates depending upon a variety of inputs, including, for example, those fuel control systems disclosed in U.S. Pat. No. 6,644,009 B2 issued to Myers, U.S. Pat. No. 6,584,762 B2 issued to Snow et al., U.S. Pat. No. 6,568,189 B2 issued to Blot-Carretero et al., and U.S. Pat. No. 4,344,141 issued to Yates.
One conventional fuel control system employs a sump to endure negative gravitational forces. During a long dive when the engine needs to remain powered throughout the end of the dive, the sump fuel volume can become relatively large. Sumps typically are unable to utilize the entire sump fuel volume, resulting in a substantial percentage of the sump fuel volume not being usable. To reduce the unusable portion of the sump fuel volume, alternate fuel storage systems, such as a fuel accumulator, may be employed. This may reduce the overall sump volume required, and therefore, the unusable portion of the sump fuel volume.
Although desirable results have been achieved using prior art fuel control systems, there is room for improvement. For example, the time to switch from the sump to the alternate fuel storage system (e.g. an accumulator) impacts the sizing of both the sump and the alternate system. In order to provide improved design of these components, a need exists for accurate methods and apparatus for determining the point of handover from the sump to the alternate system.